Toyota COMPUTER-CONTROLLED SYSTEM

DIAGNOSIS
- "CHECK ENGINE" Lamp and VF or VF1 Terminal Output
2 . VF OR VF1 TERMINAL OUTPU T
OUTPUT OF AIR-FUEL RATIO FEEDBACK
CORRECTION (T, TE1 or TE2 terminal off )
The air-fuel ratio feedback correction amount is
output in three or five levels from the VF or VF1
terminal of the check connector . When the value
is normal, the output is constant at 2 .5 V, but
when the output is greater than 2 .5 V, it
indicates that feedback correction is on increase
side, while an output lower than 2 .5 V indicates
that feedback correction is on decrease side .
Increasing 5
.0 V
3 .75 V
2
.5 V
1 .25 V
Decreasing
0V
OHP 9 3
On engines which include a vane type air flow
meter, when the VF voltage is other than 2 .5 V,
this voltage can be adjusted by tightening the
idle mixture adjusting screw on the air flow
m ete r .
The VF or VF1 terminal output when air-fuel
ratio feedback correction is not being performed
is either 0 V or 2 .5 V, depending on the vehicle
model .
Some vehicle models also have a VF2 terminal .
In V-type engines with a VF2 terminal, the VF1
terminal outputs information on the left bank
cylinders and the VF2 terminal outputs
information on the right bank cylinders .
In in-line 6-cylinder engines with a VF2 terminal,
the VF1 terminal outputs information on the No .
1 to No . 3 cylinders, and the VF2 terminal
outputs information on the No . 4 to No . 6
cylinders .
T E
1 . When adjusting the idle mixture adjusting
screw, turn it slowly, a little at a time . If
this screw is turned too quickly, air-fuel
ratio feedback correction will be halted
and you will not be able to adjust the VF
voltage .
2 . In vehicles in which the idle mixture
adjusting screw is sealed, the ECU
automatically adjusts the idle mixture
.
Therefore, it is not necessary to adjust
the idle mixture .
-REFERENCE
VF or VF1 Terminal Voltag e
When measured on an oscilloscope, the
output waveform of the VF or VF1 terminal
voltage has
a constant period of
approximately 32 msec (depending on the
engine model), as shown in the figure below .
4 V
2 V
0V
20 msec .
I I I
__ 1
+--- i
32 msec .
When a voltmeter is used to measure the
value, a virtually constant value is displayed .
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